Electrochemical growth of the polyazulene film and its electrochemical and spectroscopic properties were studied at platinum electrodes in acetonitrile by ac impedance and in situ spectroelectrochemical techniques. During polymer growth from the acetonitrile solution containing a millimolar concentration of azulene with 0.1 M tetra-n-butylammonium perchlorate as a supporting electrolyte, absorption bands were observed at 380, 480, and 680 nm. These bands were assigned to arise from neutral oligomers, their first oxidation products, and their second oxidation products, respectively. When the polymer film was oxidized in acetonitrile after the polymer is fully grown, absorption bands were red shifted significantly to 580 and around 800 nm, respectively, suggesting that the absorption bands are dependent on the chain lengths.